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Microdeletion Syndromes

  1. Anne Slavotinek

Published Online: 15 JAN 2012

DOI: 10.1002/9780470015902.a0005549.pub2

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eLS

How to Cite

Slavotinek, A. 2012. Microdeletion Syndromes. eLS. .

Author Information

  1. University of California, San Francisco, USA

Publication History

  1. Published Online: 15 JAN 2012

Abstract

A microdeletion syndrome is the clinical consequence of a submicroscopic chromosome deletion leading to monosomy for a small chromosomal segment. The clinical pictures of well-known microdeletion syndromes are relatively specific and the phenotypic characteristics were often recognised before the causal microdeletions were identified. In recent years, the widespread use of array comparative genomic hybridisation (array CGH) has lead to the discovery of numerous novel microdeletion and microduplication syndromes that were clinically delineated only after the chromosome aberration was ascertained by array. The newer microdeletion syndromes are more likely to be rare and to have milder, less specific clinical features, such as developmental delays and behavioural differences. Many of the phenotypes are still evolving. It is also becoming clear for some of the smaller deletions that the same microdeletions can be present in normal individuals and that they thus can be considered to be susceptibility factors for the development of neurocognitive differences.

Key Concepts:

  • There are numerous novel microdeletion and microduplication syndromes that have been identified and characterised after the use of array comparative genomic hybridisation (array CGH) became widespread.

  • Many microdeletion syndromes have a corresponding microduplication syndrome that is generally rarer and associated with a milder phenotype; the phenotypes of many of the newer microdeletion and microduplication syndromes are still evolving.

  • Low copy repeats (LCRs) predispose to chromosome deletions and duplications through nonallelic homologous recombination (NAHR), and many of the copy number variable regions that result in microdeletion or microduplication syndromes are situated between blocks of LCRs.

  • Most of the smaller microdeletions that were identified by array CGH have milder dysmorphic features that are less likely to be recognisable as a distinct phenotype; these microdeletions are also more likely to have been inherited from a normal or mildly affected parent.

  • Individuals with small microdeletions can still have a ‘chromosomal’ presentation that is developmental differences and intellectual disability, growth differences, behavioural problems, feeding difficulties, low muscle tone, seizures, dysmorphic features and a pattern of varying malformations.

Keywords:

  • contiguous gene syndrome;
  • haploinsufficiency;
  • microdeletion;
  • array CGH